Steering system for a hydraulic drive apparatus

ABSTRACT

An electronic steering control system for controlling the lateral movement of a vehicle powered by a pair of hydrostatic drive devices, where the system controls a pair of actuators. Each actuator is configured to move a control member associated with one of the hydrostatic drive devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/375,736, filed on Mar. 15, 2006, which is a continuation of U.S.patent application Ser. No. 10/963,109, filed on Oct. 12, 2004 now U.S.Pat. No. 7,073,330, which claims the benefit of U.S. Non-ProvisionalPatent Application Ser. No. 60/511,582, filed Oct. 15, 2003. Both ofthese prior applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to hydrostatic transaxles.

Hydrostatic transaxles (“HSTs”), including integrated hydrostatictransaxles (“IHTs”), are known in the art and are more fully describedin, among others, U.S. Pat. No. 5,314,387, which is incorporated hereinby reference in its entirety. Generally, an HST includes a centersection or the like on which is mounted a hydraulic pump and a hydraulicmotor. The hydraulic pump and the hydraulic motor each carry a pluralityof reciprocating pistons that are in fluid communication through portingformed in the center section. As the hydraulic pump rotates, the pumppistons move axially as they bear against an adjustable swash platewhere the degree of axial movement depends upon the angular orientationof the swash plate. Axial movement of the pump pistons forces ahydraulic fluid through the porting, which forces the motor pistonsagainst a thrust bearing to thereby rotate the hydraulic motor. As thehydraulic motor rotates, hydraulic fluid is returned to the hydraulicpump through the porting. In this manner, the rotation of the hydraulicpump is translated to the hydraulic motor and the rotation of thehydraulic motor may be used to drive one or more axles of a riding lawnmower, small tractor, or the like.

Zero-turn, hydrostatic transaxles (HZTs) are also known in the art.Generally, an HZT is utilized in connection with a vehicle to providefor the independent control of each of the drive wheels of the vehicle.By way of example, HZTs are described in U.S. Pat. No. 5,078,222, whichis incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

A steering mechanism for a pair of hydrostatic devices in the form ofzero-turn, hydrostatic transaxles (HZTs) that may be joined to form anintegrated, zero-turn, hydrostatic transaxle is disclosed. The steeringmechanism may comprise a steering wheel. While the described hydrostaticdevices are in the form of transaxles, the disclosed invention may beused with a variety of hydrostatic devices, including separate hydraulicpumps and hydraulic wheel motors, as would be understood by one ofordinary skill in the art.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forthillustrative embodiments that are indicative of the various ways inwhich the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had topreferred embodiments shown in the following drawings in which:

FIG. 1 illustrates a perspective view of an exemplary, integrated,zero-turn, hydrostatic transaxle constructed in accordance with theprinciples of the subject invention further illustrating an exemplary,outboard, disk brake mechanism and various casing attachment mechanisms;

FIG. 2 illustrates a perspective view of the integrated, zero-turnhydrostatic transaxle of FIG. 1 with an exemplary bracket attachmentmechanism;

FIG. 3 illustrates a perspective view of the integrated, zero-turnhydrostatic transaxle of FIG. 1 with an exemplary, inboard, disk brakemechanism;

FIG. 4 illustrates an exploded view of exemplary casing members andcenter sections of the integrated, zero-turn hydrostatic transaxle ofFIG. 1;

FIG. 5 illustrates an exploded view of the integrated, zero-turnhydrostatic transaxle of FIG. 3 particularly illustrating the exemplary,inboard, disk brake mechanism and attachment hardware;

FIG. 6 illustrates a perspective view of a further exemplary embodimentof the integrated, zero-turn hydrostatic transaxle of FIG. 1 wherein asingle plate replaces the cap members of the casings;

FIG. 7 illustrates a perspective view of yet another exemplaryembodiment of the integrated, zero-turn hydrostatic transaxle of FIG. 1wherein a single internal plate 15 replaces the cap members of thecasings;

FIG. 8 illustrates an exploded view of the integrated, zero-turnhydrostatic transaxle of FIG. 6;

FIG. 9 illustrates an exploded view of the integrated, zero-turnhydrostatic transaxle of FIG. 7;

FIG. 10 illustrates a perspective view of an exemplary, zero-turn,hydrostatic transaxle used to form the integrated zero-turn, hydrostatictransaxle of FIG. 1 further illustrating an exemplary, inboard, diskbrake mechanism and outboard control arm mechanism;

FIG. 11 illustrates a perspective view of the exemplary zero-turn,hydrostatic transaxle of FIG. 10 further illustrating an exemplary,inboard, cog brake mechanism and outboard control arm mechanism;

FIG. 12 illustrates a perspective view of the exemplary, zero-turn,hydrostatic transaxle of FIG. 10 further illustrating an exemplary,inboard, disk brake mechanism and inboard control arm mechanism;

FIG. 13 illustrates a top view of the exemplary, zero-turn, hydrostatictransaxle of FIG. 12;

FIG. 14 illustrates a perspective view of the exemplary, zero-turn,hydrostatic transaxle of FIG. 10 further illustrating an exemplary,outboard, disk brake mechanism and outboard control arm mechanism;

FIG. 15 illustrates a top view of the exemplary, zero-turn, hydrostatictransaxle of FIG. 14;

FIG. 16 illustrates a side view of the exemplary, zero-turn, hydrostatictransaxle of FIG. 12 with the cap member removed;

FIG. 17 illustrates an exploded view of the exemplary, zero-turn,hydrostatic transaxle of FIG. 12 particularly illustrating an exemplarycenter section, filter mechanism, and attachment hardware;

FIG. 18 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line A-A of FIG. 15 with an exemplary,outboard control arm mechanism and outboard brake mechanism;

FIG. 19 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line A-A of FIG. 15 with an exemplary,inboard control arm mechanism and inboard brake mechanism;

FIG. 20 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line B-B of FIG. 15;

FIG. 21 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line C-C of FIG. 13;

FIG. 22 illustrates a cross-sectional view of the exemplary, zero-turn,hydrostatic transaxle along line D-D of FIG. 13;

FIG. 23 illustrates an exploded view of an exemplary bypass mechanismand internal expansion tank cover for use in connection with theintegrated, zero-turn, hydrostatic transaxle of FIG. 1;

FIG. 24 illustrates a pump end view of exemplary center sections for usein connection with the integrated, zero-turn, hydrostatic transaxle ofFIG. 1;

FIG. 25 illustrates a motor end view of the exemplary center sections ofFIG. 24;

FIG. 26 illustrates a top view of the exemplary center sections of FIG.24;

FIG. 27 illustrates a cross-sectional view of the exemplary centersections along lines E-E of FIG. 26;

FIG. 28 illustrates an exploded view of an exemplary filter assembly foruse in connection with the integrated, zero-turn hydrostatic transaxleof FIG. 1;

FIG. 29 illustrates a side view of a vehicle incorporating an electronicsteering control system in association with a first transaxleembodiment;

FIG. 30 depicts a plan view of the vehicle embodiment shown in FIG. 29with certain elements removed for clarity;

FIG. 31 depicts a mechanical schematic of an exemplary embodiment of theelectronic steering control system shown in FIG. 29 in communicationwith a right and left zero-turn hydrostatic transaxle of a secondtransaxle embodiment;

FIG. 32 depicts a second embodiment of the steering position indicator;and

FIG. 33 illustrates a flow chart with an exemplary series of steps thatmight be utilized in connection with the operation of the electronicsteering control system shown in FIGS. 29-32.

DETAILED DESCRIPTION

Turning now to the figures, wherein like reference numerals refer tolike elements, there is illustrated a zero-turn, hydrostatic transaxlegenerally used to drive a vehicle, such as a walk behind mover, snowthrower, riding mower, tractor, or other vehicle desiring a zero turnradius. As particularly illustrated in FIGS. 1-9, the zero-turn,hydrostatic transaxle is comprised of a pair of generally mirror imageHZTs 10L and 10R that are each used to independently drive a single axleshaft 24. While HZTs 10L and 10R can be used independently, HZTs 10L and10R may be adapted to be attached to one another in a manner describedhereinafter to form an integrated, zero-turn, hydrostatic transaxle.

As will be understood by those of skill in the art, and as particularlyillustrated in FIGS. 16-22, each HZT 10 generally operates on theprinciple of an input shaft 12 rotatably driving a hydraulic pump 14which, through the action of its pump pistons 16, pushes hydraulic fluidto a hydraulic motor 18 through porting formed in a center section tocause the rotation of hydraulic motor 18. The rotation of hydraulicmotor 18 causes the rotation of a motor shaft 22 which rotation iseventually transferred through a gearing system or the like to driveaxle shaft 24. A motive force from, for example, an engine may besupplied directly to input shaft 12 or indirectly by means of a pulley26. For a more detailed description of the principles of operation ofsuch a hydrostatic transaxle, the reader is referred to U.S. Pat. Nos.5,201,692 and 6,122,996 which are incorporated herein by reference intheir entirety.

To house these components, each HZT 10 is provided with a casing whereinthe casings of each HZT 10L and 10R are generally mirror images of oneanother. In one embodiment, the casing is comprised of first casingmembers 28L and 28R and second casing members 30L and 30R (in the formof end caps) that are joined along a substantially vertical junctionsurface 32, as is illustrated in FIGS. 1-4. In this embodiment, foraccepting fasteners 52, each HZT 10 can be provided with a plurality ofbosses 54 (illustrated as three by way of example only) having fasteneraccepting openings. The fasteners 52 are passed through the fasteneraccepting openings of adjacent bosses 54 (which may be formed in boththe first and second casing sections or one of the casing sectionsalone) to mate HZTs 10L and 10R to form the integrated unit. The casingof each HZT 10L and 10R can also be provided with a flat surface 56 thatengages flat surface 56 of the opposite HZT 10 to provide an additionalpoint of contact between HZTs 10. Thus, individual HZTs 10L and 10R alsomay be joined along a substantially vertical junction surface to therebyform the integrated, zero-turn, hydrostatic transaxle assembly.

To maintain the attachment between HZTs 10L and 10R, a bracket 58 may befastened between each of the HZT casings as illustrated in FIGS. 1-3.For this same purpose and by way of further example, a rod 59 havingopposing threads that are adapted to engage correspondingly threadedapertures formed in the casings of HZTs 10 may be utilized. Stillfurther, a threaded rod may pass through un-threaded openings in thecasings and nuts may be threaded to the rod to maintain the attachmentbetween HZTs 10. In yet another configuration, one or more bosses on thefront portions of the casings of HZTs 10 may be fastened to a vehicleframe to resist torque induced by movement of axle shafts 24 andmaintain the orientation of HZTs 10L and 10R with respect to oneanother. This fastening technique may be used alone or in conjunctionwith other fastening techniques such as aforementioned bracket 58 orthreaded rod 59.

As illustrated in FIGS. 6 and 8, the casing may alternatively bearranged such that second casing sections 30 are replaced by a single,unitary casing section 31 to which first casing sections 28 areattached. In this case, casing section 31 generally comprises a platehaving openings for accepting various fasteners and junction or sealingsurfaces 32 between casing section 31 and first casing sections 28 liein parallel, vertical planes. In this embodiment, there is minimal fluidtransfer between the two units because of the high tolerances involvedin the fit of various shafts into the bores. It will be appreciated thatthe illustrated bores need not be through holes but could be partiallybored to accept the shafts of each unit while leaving an intermediatesealing surface. Bearings may be inserted into the bores, but these mayor may not be necessary depending upon anticipated loads. Casing section31 (as well as plate member 33 described below) may be fabricated frombar stock, be die cast, or the like.

Still further, as illustrated in FIGS. 7 and 9, the casing may comprisea plate member 33 adapted to be attached over the interface of one orboth first casing sections 28 at a vertical junction surface. In thisembodiment, first casing sections 28 of both HZTs 10 would be attacheddirectly to one another at a single sealing surface using fasteners thatpass through the openings in adjacent bosses. As a result of the joiningof first casing sections 28, plate member(s) 33 would be locatedinternally with respect to attached casing sections 28. Plate member(s)33 could be used to prevent movement of fluid from one HZT 10 to theother HZT 10 or allow leakage across bearings, cross holes, portings,and/or the like to allow for a single fluid fill. In the embodimentparticularly illustrated in FIG. 8, cross holes are provided to acceptthe various shafts of HZT 10.

In each of the illustrated embodiments, vertically extending from thetop of first casing member 28 is input shaft 12 and horizontallyextending from and supported by first casing member 28 is axle shaft 24.Thus, the axis of axle shaft 24 is generally perpendicular to thesubstantially vertical junction surfaces of the casing. Similarly, theplane of pump running surface 34 of center section 20 is generallyperpendicular to the substantially vertical junction surfaces while theplane of motor running surface 36 of center section 20 is generallyparallel to the substantially vertical junction surfaces. The axis ofmotor shaft 22 is also seen to be generally parallel to the axis of axleshaft 24: It is to be understood, however, that this arrangement ofcomponents is merely illustrative and that the components can beotherwise arranged without departing from the scope of this invention.

For placing hydraulic pump 14 in fluid communication with hydraulicmotor 18, center section 20 includes hydraulic porting P, as isillustrated in FIGS. 25-28. As will be further seen in these figures aswell as FIG. 24, center sections 20L and 20R of HZTs 10L and 10R,respectively, are generally mirror images of one another. However, sinceinput shafts 24 are rotated in the same direction when the vehicle isdriven in the forward or reverse direction, the intersection of thekidneys, formed on running surface 34, and the cross passages of portingP are symmetrical as seen in FIG. 26. It will be appreciated, however,that center sections 20L and 20R can be full mirror images of oneanother in the case where the angular rotation of the swash plates ofeach HZT are made non-symmetrical, i.e., the angle of rotation of theswash pates are reversed with respect to one another.

Hydraulic porting P is in further fluid communication with a source ofmakeup fluid, such as a fluid sump or a charge gallery, for example, bymeans of check plugs 60. Generally, hydraulic porting P comprises a highpressure side through which fluid moves from hydraulic pump 14 tohydraulic motor 18 and a low pressure side through which fluid returnsfrom hydraulic motor 18 to hydraulic pump 14. Since center sections 20Land 20R are generally mirror images of one another, it will beappreciated that similar hydraulic porting P will be utilized when bothHZTs 10L and 10R are placed in the forward or reverse direction. Thisarrangement of center section porting P provides HZTs 10L and 10R withnearly identical hydraulic efficiencies.

To minimize the introduction of impurities, such as metal shavings, intothe hydraulic circuit when makeup fluid is drawn into the hydrauliccircuit, an upward facing filter assembly 62, illustrated in FIG. 28,may be positioned adjacent to center section 20 through which fluid maypass from the sump to hydraulic porting P. Upward facing filter assembly62 reduces the potential that air is ingested into hydraulic porting Pas it provides an upward facing exit path for the air. This isespecially the case when filter assembly 62 is positioned in a generallynon-turbulent area of operation within HZT 10.

For attaching center section 20 to first casing member 28, fasteners 40(e.g., bolts) may be passed through openings 42 formed in center section20 to mate with attachment points 44 (e.g., threaded holes) formed infirst casing member 28.

For adjusting the amount of oil that is pushed from hydraulic pump 14 tohydraulic motor 18 via the high pressure side of hydraulic porting P,each HZT 10 includes a moveable swash plate 74 against which pumppistons 16 travel. The direction of rotation of hydraulic pump 14 isfixed by the rotation of input shaft 12. Hydraulic pump 14 is nearlyalways rotated in one direction. As will be understood by those ofordinary skill in the art, swash plate 74 may be moved to a variety ofpositions to vary the stroke of pump pistons 16 and the direction ofrotation of hydraulic motor 18. Generally, as swash plate 74 angle isvaried in one direction from the neutral position the stroke of pumppistons 16 is varied, which then drives hydraulic motor 18 in adirection determined by the hydraulic porting at a speed determined bythe volume of the fluid displaced by pump pistons 16 and the torquedelivered by input shaft 12. As will be appreciated, rotation ofhydraulic motor 18 results from motor pistons 19 moving against a thrustbearing 76 under the influence of the hydraulic fluid. As the angle ofswash plate 74 is decreased to pass through the neutral position, thedirection of rotation of hydraulic motor 18 is reversed and the speed ofhydraulic motor 18 is again determined by the volume of fluid displacedby pump pistons 16 and the torque delivered by input shaft 12.

Since the speed of rotation of hydraulic motor 18 is dependent upon theamount of hydraulic fluid pumped thereinto by hydraulic pump 16 and thedirection of rotation of hydraulic motor 18 is dependent upon thedirection of angular rotation of swash plate 74, the positioning ofswash plate 74 is seen to control the speed and direction of rotation ofhydraulic motor 18 and, as will be apparent, the speed and direction ofrotation of axle shaft 24. While it is true that the direction ofrotation of hydraulic motor 18 will be affected by the rotation ofhydraulic pump 16, the variation of rotation from one direction toanother is accomplished completely by swash plate 74.

For moving swash plate 74, swash plate 74 is supported by a pair oftrunnion arms 78 that are rotatably supported in the casing of HZT 10 asillustrated in FIGS. 18 and 19. As will be appreciated, rotation oftrunnion arms 78 changes the angular orientation of swash plate 74 withrespect to pump pistons 16. To rotate trunnion arms 78 and, accordingly,move swash plate 74, a speed adjusting mechanism is coupled to one oftrunnion arms 78. A control arm 80 of the speed adjusting mechanism maybe connected, via a driving link, to a lever or a pedal provided on avehicle whereby movement of the lever or pedal is translated to controlarm 80 to cause the rotation of trunnion arms 78 and movement of theswash plate assembly. A further, exemplary speed adjusting mechanismwith a return-to-neutral mechanism 41 is illustrated in FIG. 8 of U.S.patent application Ser. No. 09/789,419, which is incorporated herein byreference in its entirety.

It is to be further appreciated that control arm 80 may be located oneither the outboard or inboard side of the casing of HZT 10, asillustrated in FIGS. 18 and 19, respectively. To this end, first casingmember 28 may be provided with a pair of opposed bearing seats 82 inwhich trunnion arms 78 are carried. The casing may then have openingsadjacent to both bearing seats 82, illustrated in FIG. 19, by whichcontrol arm 80 can be attached to one of trunnion arms 78. Thus,depending upon the desired location for control arm 80, control arm 80would be mated to one of trunnion arms 78 by way of one of the openingsand the opposite opening would be closed with a seal 84. Alternatively,the casing can have an opening adjacent to just one bearing seat 82, asillustrated in FIG. 18. In this case, it will be appreciated that thelocation of the single opening will dictate whether control arm 80 ismounted on the inboard side or the outboard side of the casing of HZT10. It will be further appreciated that when it is desired to have aninboard control arm 80 on an integrated, zero-turn, hydrostatictransaxle assembly, sufficient spacing is to be provided between thejoined casings of HZTs 10L and 10R, similar to but larger than thespacing illustrated in FIGS. 1 and 2. The spacing is used to accommodatecontrol arms 80 (as well as any inboard braking mechanisms that aredescribed hereinafter).

For limiting the range of motion of control arm 80, control arm 80 maybe provided with a slot 86 that cooperates with a stop 88, such as abolt or the like, attached to the casing as illustrated in FIG. 14. Itwill also be appreciated that control arm 80 may be locked into theneutral position, for example during shipment of HZT 10 and/or duringassembly into a vehicle. To this end, as illustrated in FIG. 1, a nut 90may be attached to stop 88 to frictionally engage the control armmechanism and thereby prevent its movement. Slot 86 of control arm 80may be asymmetrical to thereby allow a greater speed to be imparted toaxle 24 in the forward direction as compared to the reverse direction.

To provide a space for hydraulic fluid to expand into during operationof HZT 10, each HZT 10 may include an internally located expansion tank92 as illustrated in FIGS. 16, 17 and 23. In the illustrated embodiment,expansion tank 92 is positioned within the HZT casing adjacent to a bullgear 94 that is used to drive axle shaft 24. Venting of expansion tank92 to atmosphere is accomplished via a breather tube 96 that extendsfrom a top of the casing of HZT 10. Such an expansion tank may be seenin U.S. patent application Ser. No. 10/062,734, which is incorporatedherein by reference in its entirety. Fluid may be added to HZT 10 bymeans of an oil fill port 98 that is also formed on the top of thecasing of HZT 10. Further, expansion tank cover 91 may be provided withan indentation 93 and a thumb stop 95 (that extends below the sealingsurface) by which expansion tank cover 91 may be grasped for insertioninto first casing section 28. Indentation 93 is particularly sized toaccept a finger of the installer. In this manner, expansion tank cover91 may be installed while allowing the user to avoid contacting sealantcarried on the sealing surface of cover 91.

To enable the vehicle on which HZTs 10 are mounted to roll or“freewheel” without resistance from the hydraulic fluid, each HZT 10 mayinclude a hydraulic bypass. Generally, when an HZT 10 does not have amotive force being applied to it, hydraulic pump 14 and hydraulic motor18 are not being rotated. Therefore, any attempt to roll the vehiclewould transmit rotational energy through axle shaft 24 to motor shaft22, via any internal gearing, thereby causing hydraulic motor 18 torotate. The rotation of hydraulic motor 18, and the action of motorpistons 19 against motor thrust bearing 76, causes fluid to flow throughhydraulic porting P of center section 20 to hydraulic pump 14. However,with hydraulic pump 14 being in neutral, the resultant pressure causesresistance to motion of motor shaft 22 and axle shaft 24 and preventsthe user from easily pushing the vehicle.

To solve this problem, a bypass mechanism 100 may be associated with thehydraulic circuit to allow fluid to flow between the high pressure sideand the low pressure side of center section 20 porting. Bypass mechanism100, illustrated in FIG. 23, may be activated via rotation of a bypassarm 102 that is located proximate to the top of the casing of HZT 10.Bypass arm 102 is linked to a bypass actuator 104 that, in turn,interfaces with center section 20 at its distal end. The degree ofmovement of bypass arm 102 may be controlled by providing control arm102 with a notch 103 the shoulders of which are adapted to engage a stop105 formed on the casing to limit how far bypass arm 102 may be rotated.

To drive axle shaft 24, gearing may be provided that functions todrivingly couple axle shaft 24 to motor shaft 22. By way of example,with reference to FIGS. 16 and 17, motor shaft 22 may include a drivegear 114 that drivingly engages one or more reduction gears 116 thatdrive bull gear 94 which, in turn, drivingly engages axle shaft 24. Inthe illustrative embodiment, two reduction gears 116 a and 116 b areprovided wherein first reduction gear 116 a engages drive gear 114 anddrives second reduction gear 116 b that is set within the insidediameter of first reduction gear 116 a. Second reduction gear 116 bdrives bull gear 94.

As further illustrated in FIG. 22, a proximal end of axle shaft 24 iscarried by an inboard bushing 118 positioned within first casing section28 adjacent to bull gear 94.

Axial movement of axle shaft 24 in an inward direction towards bull gear94 is prevented since the proximal end of axle shaft 24 is restrained bycontacting an interior wall of first casing section 28. Axial movementof axle shaft 24 in an outward direction may be prevented through theuse of a retaining ring positioned adjacent to the inward side of bullgear 94. First casing section 28 also includes an axle horn in which iscarried an outboard bushing 120 that provides additional support foraxle shaft 24. A seal and retaining ring pack 122 is positioned in theaxle horn on the outboard side of bushing 120. It is to be understoodthat the distal end of axle shaft 24 is adapted to have a vehicle wheelmounted thereto.

For allowing a brake mechanism 123 to be mounted to either the inboardor outboard side of the casing of HZT 10, motor shaft 22 can extend fromthe inboard side or the outboard side of first casing section 28, asseen in FIGS. 20 and 21. It will be appreciated that brake mechanism 123may be a disc brake mechanism, as illustrated in FIG. 10, a coggedparking brake as illustrated in FIG. 11, or the like. As furtherillustrated in FIGS. 20 and 21, motor shaft 22 may be provided with aconfiguration that depends upon whether brake mechanism 123 is to bemounted on the inboard or outboard side of the casing. In this regard,three motor/brake shaft options are available. First, the motor/brakeshaft could extend simultaneously from both the inboard and outboardside of the casing of HZT 10 (not shown). Second, as illustrated in FIG.21, second casing section 30 can have an opening to accommodate motorshaft 22 for inboard mounting thereof and the motor/brake shaft wouldnot extend through first casing section 28. Third, as illustrated inFIG. 20, second casing section 30 can be used to cover and support oneend of motor/brake shaft 22 while the opposite end of the motor/brakeshaft 22 extends from first casing section 28 to the outboard side ofHZT 10. It will be appreciated that the first option increases theflexibility of HZT 10 while the second and third options provide for alower cost motor/brake shaft while eliminating the need for extramachining and seals.

To provide for the easy mounting of HZT 10 to a vehicle frame, firstcasing section 28 of each HZT 10 includes a plurality of fasteneraccepting openings 142. As illustrated in FIGS. 12-15, a pair offastener accepting openings 142 can be positioned on opposing sides offirst casing section 28 and a further plurality of fastener acceptingopenings 142 can be positioned on the axle shaft horn of first casingsection 28. While illustrated with four fastener accepting openings 142being formed on the axle shaft horn of first casing section 28, it is tobe appreciated that this is not intended to be limiting. Rather, anynumber of fastener accepting openings 142 can be formed and/or utilizedin the attachment process. Still further, fastener accepting openingscould be formed on a bracket 58 for use in mounting HZTs 10L and 10R toa vehicle frame.

For use in cooling the HZTs 10L and 10R, a fan 150 may be mounted to oneor both input shafts 12 adjacent to pulley 26 as is illustrated in FIGS.1 and 3. When two fans 150 are utilized, the diameters of fans 150 needto be such that they do not contact each other while turning.Alternatively, if fans 150 do have overlapping diameters, fans 150 needto be vertically spaced to prevent blade contact.

For controlling the movement of a vehicle 198 incorporating a zero-turnhydrostatic transaxle in a lateral direction, an electronic steeringcontrol system 200 may be provided, which includes a steering mechanism202 that enables a vehicle operator to indicate the direction in whichthey desire the vehicle to move. As shown in FIGS. 29-32, steeringmechanism 202 may be a standard circular steering wheel; however, itshould be understood that the shape of the steering wheel is notimportant as long as the functionality provided by the steering wheel ismaintained. Steering mechanism 202 is also connected to steering column204 and steering column 204 cooperates with a steering position detector206. Steering position detector 206 senses the rotational position ofsteering column 204. A signal representing the rotational position ofsteering column 204 is then transmitted to a computer processor 222,which then determines whether the position of steering column 204 haschanged, and in which direction the change has occurred. The rotationalposition of steering column 204 may be detected by using sensors 208located within steering position detector 206 that are capable ofdetermining the rotational position of steering column 204 with respectto a fixed point, such as hall sensors, variable resistors, etc.Therefore, after a vehicle operator rotates steering mechanism 202 in aparticular direction, steering position detector 206 determines therotational position of steering column 204 with respect to that fixedpoint.

As previously noted, to ensure that vehicle 198 is steered in the properdirection, sensors 208 may send a signal to a computer processor 222,the signal being representative of the rotational position of thesteering mechanism. As shown in FIG. 31, computer processor 222 may beelectrically connected to steering position detector 206 and sensors208. However, if computer processor 222 is not located proximate to andelectrically connected to steering mechanism 202, sensors 208 may beconnected to transmitter 210, shown in FIG. 32, which would transmit thesignals provided by sensors 208 to computer processor 222. Therefore, itshould be appreciated that computer processor 222 may be located invarious positions on vehicle 198.

Other elements are shown in FIGS. 29-32 that are generally necessary forfunctioning of vehicle 198 and electronic steering control system 200,as would be understood by a person of ordinary skill in the art. Abattery 212 would generally be required for powering various vehiclesystems, including electronic steering control system 200. Otherelements such as ignition switch 214 and operator speed control 190would also be required.

FIGS. 29-31 also depict two transaxle configuration embodiments. In thefirst embodiment shown in FIGS. 29 and 30, HZT 196 is of a unitarydesign wherein all elements are contiguous and may share oil. In thesecond embodiment shown in FIG. 31, HZTs 10R and 10L are separate unitsthat may be individually mounted in a vehicle or attached to each otherand then mounted in a vehicle. Electronic steering control system 200 isamenable to a variety of transaxle configurations wherein there are twoindependently drivable transaxles.

FIG. 33 depicts a flowchart exemplifying the operation of the electronicsteering control system described above. For example, if ignition switch214 is activated by a vehicle operator (step 300), vehicle 198 may firstdetermine whether the vehicle is safe for operation (step 302). Step 302may include testing to see if control arms 80L and 80R, or control arms180L and 180R, and swash plates 74L and 74R are in the neutral position,brake mechanism 123 is engaged, the vehicle operator is seated on thevehicle or the mower 192 is turned off.

Once it is determined that vehicle 198 is safe for operation, vehicleengine 194 will be started (step 304). Then electronic steering controlsystem 200 will determine if speed control 190 has been adjusted (step306). The speed of vehicle 198 will be directly proportional to theposition of speed control 190, which cooperates with swash plate 74 tocontrol the speed of vehicle 198. If speed control 190 has beenadjusted, electronic control system 200 will then determine whethersteering mechanism 202 has been rotated (step 312). If speed control 190has been moved and steering mechanism 202 has not been rotated, anelectronic control unit 220 will cause HZT 10L and 10R to drive axleshaft 24 at a speed that correlates to the position of speed control 190(step 314). If speed control 190 has not been adjusted, electronicsteering adjustment system 200 will determine whether steering mechanism202 has been rotated (step 308). If speed control 190 has not beenadjusted and steering mechanism 202 has been adjusted, electronicsteering adjustment system 200 will determine if speed control 190 is inneutral (step 309). If speed control 190 is in neutral, step 310 and thesteps that follow it will be executed. If speed control 190 is not inneutral, step 316 and the steps that follow it will be employed.

If steering mechanism 202 is rotated, electronic steering control system200 will determine whether steering mechanism 202 was rotated to theright (step 316). If steering mechanism 202 was rotated to the right,computer processor 222 will determine the speed at which the vehicle isset and the degree to which steering mechanism 202 has been rotated.Based on these factors and in response to steering mechanism 202 beingrotated to the right, the computer processor 222 sends a signal toactuators 220 to adjust the speed of axle shaft 24 for each HZT 10L and10R wherein the speed of axle shaft 24 of HZT 10R will have a lowerspeed than axle shaft 24 of HZT 10L, which causes vehicle 198 to besteered to the right (step 322).

If steering mechanism 202 was not rotated to the right, the electronicsteering control system 200 will determine if steering mechanism 202 wasrotated to the left (step 318). If steering mechanism 202 is rotated tothe left, computer processor 222 will determine the speed at which thevehicle is set and the degree in which steering mechanism 202 has beenrotated. Based on these factors and in response to steering mechanism202 being rotated to the left, computer processor 222 will send a signalto actuators 220 to adjust the speed for axle shaft 24 for each HZT 10Land 10R, wherein the speed of axle shaft 24 of HZT 10L will have a lowerspeed than axle shaft 24 of HZT 10R, which causes vehicle 198 to steerto the left (step 320).

If speed control 190 has not been adjusted and steering mechanism 202has not been rotated, electronic steering control system 200 willdetermine whether vehicle ignition 214 has been disabled (step 310). Ifvehicle ignition 214 has not been disabled, vehicle 198 will repeat thesteps described above of determining whether speed control 190 has beenmoved or steering mechanism 202 has been rotated, beginning with step306. If vehicle ignition 214 has been disabled, engine 194 will bedisabled (step 330).

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangement disclosed is meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalents thereof.

1. A control apparatus for a vehicle, comprising: a first continuouslyvariable axle driving apparatus mounted to the vehicle and having aneutral condition and a plurality of forward output speeds and aplurality of reverse output speeds; a first control mechanism inmechanical communication with the first continuously variable axledriving apparatus, the first control mechanism movable to causeadjustment of the output speed of the first continuously variable axledriving apparatus and to allow placement of the first continuouslyvariable axle driving apparatus in the neutral condition; a secondcontinuously variable axle driving apparatus mounted to the vehicle andhaving a neutral condition and a plurality of forward output speeds anda plurality of reverse output speeds; a second control mechanism inmechanical communication with the second continuously variable axledriving apparatus, the second control mechanism movable to causeadjustment of the output speed of the second continuously variable axledriving apparatus and to allow placement of the second continuouslyvariable axle driving apparatus in the neutral condition; a speedadjusting mechanism mounted to the vehicle and in communication with thefirst and second control mechanisms, the speed adjusting mechanismadjustable to cause simultaneous movement of the first and the secondcontrol mechanisms to establish generally equivalent output speeds ofthe first and the second continuously variable axle driving apparatuses;and a steering mechanism mounted to the vehicle and in communicationwith the first and second control mechanisms, the steering mechanismadjustable to cause movement of the first and the second controlmechanisms, thereby adjusting the output speeds of the first and thesecond continuously variable axle driving apparatuses such that when theoutput speed of one of the continuously variable axle drivingapparatuses is increased the output speed of the other of thecontinuously variable axle driving apparatuses is decreased, and suchthat when the output speed of one of the continuously variable axledriving apparatuses is decreased the output speed of the other of thecontinuously variable axle driving apparatuses is increased, therebycausing steering of the vehicle in response to the adjustment of thesteering mechanism; and the steering mechanism is prevented from movingthe first and the second control mechanisms if the first continuouslyvariable axle driving apparatus and the second continuously variableaxle driving apparatus are each in their respective neutral conditions.2. The control apparatus as set forth in claim 1, wherein the firstcontinuously variable axle driving apparatus and the second continuouslyvariable axle driving apparatus each comprise a hydrostatic transaxle.3. The control apparatus as set forth in claim 1, wherein the firstcontrol mechanism and the second control mechanism each comprise atrunnion arm.
 4. The control apparatus as set forth in claim 3, whereinthe first control mechanism and the second control mechanism eachcomprise a control arm.
 5. The control apparatus as set forth in claim1, wherein the speed adjusting mechanism comprises a foot pedal.
 6. Thecontrol apparatus as set forth in claim 1, wherein the steeringmechanism comprises a steering wheel.
 7. The control apparatus as setforth in claim 1, further comprising an electronic processor incommunication with the speed adjusting mechanism, the steeringmechanism, and the first and the second control mechanisms.
 8. Thecontrol apparatus as set forth in claim 7, wherein a control signal inresponse to adjustment of the speed adjusting mechanism and a controlsignal in response to adjustment of the steering mechanism are receivedby the processor and processed to cause adjustment of the first and thesecond control mechanisms.
 9. The control apparatus as set forth inclaim 7, wherein the processor will prevent operation of the vehicle ifan unsafe condition exists.
 10. A control apparatus for a vehicle,comprising: a first continuously variable axle driving apparatus mountedto the vehicle and having a neutral condition and a plurality of forwardoutput speeds and a plurality of reverse output speeds; a first controlmechanism in mechanical communication with the first continuouslyvariable axle driving apparatus, the first control mechanism movable tocause adjustment of the output speed of the first continuously variableaxle driving apparatus and to allow placement of the first continuouslyvariable axle driving apparatus in the neutral condition; a secondcontinuously variable axle driving apparatus mounted to the vehicle andhaving a neutral condition and a plurality of forward output speeds anda plurality of reverse output speeds; a second control mechanism inmechanical communication with the second continuously variable axledriving apparatus, the second control mechanism movable to causeadjustment of the output speed of the second continuously variable axledriving apparatus and to allow placement of the second continuouslyvariable axle driving apparatus in the neutral condition; a speedadjusting mechanism mounted to the vehicle and in communication with thefirst and second control mechanisms, the speed adjusting mechanismadjustable to cause simultaneous movement of the first and the secondcontrol mechanisms; and a steering mechanism mounted to the vehicle andin communication with the first and second control mechanisms, thesteering mechanism adjustable to cause opposite movement of the firstand the second control mechanisms; wherein the output speed of the firstcontinuously variable axle driving apparatus and the output speed of thesecond continuously variable axle driving apparatus are established bycombining the required movement dictated by the speed adjustingmechanism and the steering mechanism; and wherein the steering mechanismis prevented from moving the first and the second control mechanisms ifthe first continuously variable axle driving apparatus and the secondcontinuously variable axle driving apparatus are each in theirrespective neutral conditions.
 11. The control apparatus as set forth inclaim 10, wherein the first continuously variable axle driving apparatusand the second continuously variable axle driving apparatus eachcomprise a hydrostatic transaxle.
 12. The control apparatus as set forthin claim 10, wherein the first control mechanism and the second controlmechanism each comprise a trunnion arm.
 13. The control apparatus as setforth in claim 12, wherein the first control mechanism and the secondcontrol mechanism each comprise a control arm.
 14. The control apparatusas set forth in claim 10, wherein the speed adjusting mechanismcomprises a foot pedal.
 15. The control apparatus as set forth in claim10, wherein the steering mechanism comprises a steering wheel.
 16. Thecontrol apparatus as set forth in claim 10, further comprising anelectronic processor in communication with the speed adjustingmechanism, the steering mechanism, and the first and the second controlmechanisms.
 17. The control apparatus as set forth in claim 16, whereina control signal in response to adjustment of the speed adjustingmechanism and a control signal in response to adjustment of the steeringmechanism are received by the processor and processed to causeadjustment of the first and the second control mechanisms.
 18. Thecontrol apparatus as set forth in claim 16, wherein the processor willprevent operation of the vehicle if an unsafe condition exists.
 19. Acontrol apparatus for a vehicle, comprising: a first continuouslyvariable axle driving apparatus mounted to the vehicle and having aneutral condition and a plurality of forward output speeds and aplurality of reverse output speeds; a first control mechanism inmechanical communication with the first continuously variable axledriving apparatus, the first control mechanism movable to causeadjustment of the output speed of the first continuously variable axledriving apparatus and to allow placement of the first continuouslyvariable axle driving apparatus in the neutral condition; a firstelectric actuator in mechanical communication with the first controlmechanism; a second continuously variable axle driving apparatus mountedto the vehicle and having a neutral condition and a plurality of forwardoutput speeds and a plurality of reverse output speeds; a second controlmechanism in mechanical communication with the second continuouslyvariable axle driving apparatus, the second control mechanism movable tocause adjustment of the output speed of the second continuously variableaxle driving apparatus and to allow placement of the second continuouslyvariable axle driving apparatus in the neutral condition; a secondelectric actuator in mechanical communication with the second controlmechanism; a speed adjusting mechanism attached to the vehicle andmovable to cause simultaneous movement of the first electric actuatorand the second electric actuator; and a steering mechanism attached tothe vehicle, wherein adjustment of the steering mechanism causes thefirst electric actuator and the second electric actuator to be moved inopposite directions; wherein the output speed of the first continuouslyvariable axle driving apparatus and the output speed of the secondcontinuously variable axle driving apparatus are established by blendingthe required movement of the first and the second electric actuatorsdictated by both the speed adjusting mechanism and the steeringmechanism; and wherein the steering mechanism is prevented from causingmovement of the first electric actuator and the second electric actuatorif the speed adjusting mechanism has dictated placement of the firstcontinuously variable axle driving apparatus and the second continuouslyvariable axle driving apparatus in their respective neutral conditions.20. The control apparatus as set forth in claim 19, further comprising aprocessor.
 21. The control apparatus as set forth in claim 20, wherein acontrol signal in response to adjustment of the speed adjustingmechanism and a control signal in response to adjustment of the steeringmechanism are received by the processor and processed to causeadjustment of the positions of the first electric actuator and thesecond electric actuator.
 22. The control apparatus as set forth inclaim 20, wherein the processor will prevent operation of the vehicle ifan unsafe condition exists.